Can you post the objection that was raised about this exactly? There’s various things that could apply here, it would help to know which one specifically is being raised as an issue.
Some thoughts:
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both SIFT and iFOD2 were originally proposed on single-shell HARDI data. There’s no issue there. Both of these rely on the availability of adequate fODFs, so the question really reduces to whether the fODF produced by CSD (and now multi-tissue CSD, even from single-shell data) are suitable for the purposes of SIFT and iFOD2.
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Your data already qualify as HARDI - 55 directions is well within the HARDI range. The main difference here is the use of a lower b-value than we’ve used in previous publications. This may influence interpretation of the results, but most likely in a relatively subtle way (see e.g. this post). But I certainly don’t see it being problematic either for SIFT or iFOD2.
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One consequence of lower b-values is that the GM signal is higher than it would be at higher b-values, which introduces more scope for spurious connections through the grey matter. But high b-values are not immune to this problem, and these days, ACT is by far the better approach to dealing with this anyway.
But otherwise, there is nothing inherently wrong with using SIFT or iFOD2 on your data – I’m sure plenty of users already do with similar data… It might not be the absolute best that can be done nowadays, but it’s certainly feasible. How well this works will overwhelmingly depend on your image quality, SNR in particular. You have sufficient angular coverage already (see e.g. this paper on the topic if you’re interested), the thing that matters now is whether you have adequate contrast to noise ratio (CNR). You won’t have as much contrast at b=1000 as you might at b=3000, but if your SNR is sufficient, that will help regain the CNR. I’d give it a shot and see how well it works.